全国免费服务热线：

888-888-8888

Bird flu resurfaces in China

日期：2019-03-02 10:07:04 作者：薛幸 阅读：

By Debora MacKenzie China has reported its first outbreak of H5N1 bird flu since it brought a widespread epidemic in poultry under control in 2004. This time, the virus has been found in wild geese in a nature reserve. Scientists consider it unlikely that the geese carried H5N1 into China, though this cannot be ruled out. Instead, the deaths could show that, even though China has not reported any recent outbreaks, H5N1 is continuing to circulate in its domestic poultry. On 4 May, 178 bar-headed geese which had just completed their arduous annual migration over the Himalayas from northern India died at Qinghai Lake Nature Reserve in western China. After initial denials, on 22 May the Chinese Ministry of Agriculture announced that the birds had died of H5N1. It is vaccinating all poultry in the region, and has closed nature reserves to the public. H5N1 bird flu caused massive outbreaks in poultry across east Asia in early 2004, and it is now spreading again in Vietnam. Official figures put the human death toll so far at 53. In Geneva this week the World Health Organization renewed warnings that the virus could evolve into a human pandemic. In 2004, China initially denied it had any H5N1, but admitted outbreaks shortly after New Scientist reported scientists’ suspicions that the H5N1 in Thailand and Vietnam originated in China. Chinese scientists later published evidence that the strain emerged in China. China brought the disease under control in March 2004 by destroying nine million birds. It reported only 49 outbreaks, in contrast to Thailand and Vietnam with over a thousand each. But, unlike those countries, China practices widespread poultry vaccination for H5N1. Without very stringent controls, such vaccination can prevent visible outbreaks, while still allowing the virus to persist silently. And ducks can carry bird flu without showing symptoms. H5N1 might therefore be widespread in Chinese poultry, despite the lack of reported cases. China has reported only one outbreak since March 2004 – in July, in Anhui province. The authorities blamed this occurrence on wild waterfowl on a nearby lake. But Albert Osterhaus, a leading flu expert at the University of Rotterdam in the Netherlands, told New Scientist that it is rare to find such highly pathogenic strains of bird flu in wild fowl. As for the geese in Qinghai, he says, “we can’t be sure until we see the genetic sequence, but it is not unlikely that these cases are spillback from local poultry”. The geese could have become infected by swimming in ponds used by infected local birds. In 2003, says Osterhaus, when Dutch poultry was hit by another highly pathogenic bird flu called H7, swans using the same pond as infected farm birds caught the H7 virus. The geese could have carried the flu with them from India only if it did not make them ill at all. “We don’t know what H5N1 does in these geese,” says Osterhaus. Richard Thomas of Bird Life International, a conservation organisation, says the stress of their migration, during which they reach altitudes over 10,000 metres, could in theory have caused the geese to fall ill on arrival with a virus that would previously not have affected them. But no reports of H5N1 have been confirmed in India, says Osterhaus. The exhausted birds would also have been easy prey for a flu virus they met in China,